1. Field of the Invention
The present invention relates to a wire electric discharge machine performing distortion removing machining.
2. Description of the Related Art
When a workpiece made of a material having a comparatively large internal stress is subjected to wire electric discharge machining, the internal stress is released according to the progress of machining, and thereby distortion is caused in the workpiece. This distortion causes a machining dimension error, so as to adversely affect the machining accuracy and the machining time. In the conventional machining method, when a material having a comparatively large internal stress is subjected to wire electric discharge machining, a machining process causing distortion is performed so as to leave a machining margin corresponding to an anticipated amount of the distortion, and then a machining process to remove the distortion is performed (see, for example, Japanese Patent Application Laid-Open No. 55-137834).
However, the amount of distortion, and the portion of the workpiece, in which portion the distortion is caused, are not known before the machining process, and hence the anticipated machining margin needs to be set large. For this reason, rough machining is performed twice, and hence machining time is significantly increased. In the case of machining a mold, single-piece machining is performed in many cases, and hence the conventional machining method causes almost no problem. However, in some cases of machining a machine component and an electrical component, a large number of components having the same shape are machined. In these cases, machining time is significantly increased, and hence a machining method which can reduce the machining time is desired.